The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
In the fields of image sensors or optical sensors, a variety of techniques using a sensor capable of sensing photons having an infrared, visible or wide spectrum have been developed. However, not one of the techniques has been applied to mass production of an imaging device that is fundamentally a three-dimensional multi-layer structure capable of sensing signals of many different wavelengths at various layers as an analog of photographic color film.
This before mentioned integration has not been accomplished because each technique has limitations that prevent integration into a three dimensional layered structure, problems such as 1) reduced fill factor (where 100% fill factor means all incident light goes into signal detection) due to the existence of signal processing and transfer circuits taking area away from photon collection, 2) that light of a variety of wavelengths is not sensed at one pixel location (through the use of a Color filter array on a black and white sensor), 3) the ability to independently optimize the collection wavelength filter characteristics from the device structure by using a filter that is integrated into a device and can select specific ranges of wavelengths, 4) solutions to issues with leakage current problems (also known as dark current) in an optical sensor structure that cannot be used in a three dimensional layered structure, and 5) issues with noise cancellation in the sensor because of limited process options or limited circuitry space.
In above-mentioned sensor, the three-dimensional multi-layer structure is required in order to sense various spectrums at one pixel location. However, a complete three-dimensional multi-layer thin film structure has not been successfully commercialized. This is because each previous technique has problems, such as a misalignment between layers, problems caused by using a glass or quartz crystal substrate (and the subsequent thermal coefficient of expansion problems), and the method was unknown as to how to separate semiconductor layers by inserting dielectric between them.
One limiting factor in a traditional planar image sensor; Is that, in order to obtain a color selective output signal from the sensor, a color filter array must be used. The color filter array is patterned across the planar Black and white sensor in various patterns with the Bayer sensor pattern being one of the most common. In this case, a significant part of incident light is lost. In most cases, about ⅔ of incident light is absorbed and only ⅓ of incident light is converted into picture information at a given pixel. A sensor having three or more laminated photodiodes can convert the whole light illuminated thereon into picture information like photographic film without subsequent photon loss.
Fill factor refers to the ratio of pixel area in which incoming photons can be collected and converted into signals to the area used for support circuits and semiconducting structures A fill factor of 100% can be obtained using only a full frame CCD. In a sensor having a fill factor of less than 100% the portion that is not used as the image region, of the pixel directly degrades the collecting efficiency of the sensor. In an ILT (interline transfer) CCD the fill factor of less than 100% is due to the vertical transfer semiconducting structure. In a CMOS APS, the region that holds the amplifier and readout transistors and metal interconnects takes away from the light collection area that can be used for the photon detection.